Nerfed Burst of Flames and Backstab; Buffed Tools

New reward calculations for Backstab, as proposed by @ShabbyX
Changed Burst of Flames damage to 10% of INT, as proposed by @deilann
Strengthened Tools of the Trade, as proposed by @Alys
Merge branch 'skillbalancing' of https://github.com/ShilohT/habitrpg-shared into ShilohT-skillbalancing
Merge fireball (Burst of Flames) changes from 'ShilohT-skillbalancing' into rebalancing-2014-12
Merge toolsOfTrade changes from 'ShilohT-skillbalancing' into rebalancing-2014-12